-LRB- CNN -RRB- Not one , but two French citizens have been connected to beheadings in a recent ISIS video , both of them 22-year-old men who went to Syria to join the group , authorities said Wednesday .

The Paris prosecutor 's office on Wednesday identified Mickael Dos Santos , a convert to Islam from the Paris suburb of Champigny-sur-Marne who was well-known to French anti-terror authorities before the ISIS video release .

Why are so many young French turning to jihad ?

In fact , an October 2013 warrant for Dos Santos ' arrest was issued as part of an investigation into French citizens who had gone to Syria to take part in ISIS jihad there , the prosecutor 's office said .

Dos Santos joins Maxime Hauchard , who authorities said Monday was also on the video , released over the weekend , that depicts in graphic detail , the beheadings of men whom ISIS militants claim were Syrian government pilots . It also shows the aftermath of another beheading in which the victim in not clearly recognizable , but that the U.S. government says was American aid worker Peter Kassig .

Public Prosecutor Francois Molins described Hauchard -- who went to Syria in 2013 and visiting Mauritania the previous year -- is a `` self-radicalized '' jihadist who traveled to the region under the guise of a humanitarian mission . He was known to French security services as far back as 2011 , the prosecutor said .

More barbaric ISIS videos expected after Kassig 's death , analyst says

Speaking from Australia alongside Prime Minister Tony Abbott , French President FranÃ § ois Hollande said his country 's judicial system will work to establish `` exactly what role '' the two French men played , though the mere fact they came from France and became involved at all warrants attention and action .

`` We have to be even more aware , even in terms of the information that needs to be handed out , in terms of the danger that Internet sites carry and how these young people can be indoctrinated , '' Hollande said . `` They could be from any background , from any ethnic origin , but they easily can be brainwashed into becoming converts . ''

The ranks of ISIS -- the extremist group calling itself the Islamic State that 's taken over vast swaths of Syria and Iraq -- have swelled with volunteers coming from outside the region , including from the West .

How foreign fighters are bolstering ISIS

Intelligence estimates indicate that more than 100 of the foreign fighters in Iraq and Syria have come from the United States . Hundreds more arrived from Europe , including more than 900 French citizens that country 's government believes are involved in the jihad there . This influx has spurred concerns that some of these fighters could bring the fight back home , perhaps with attacks inside Western nations .

Those worries have been heightened by the group 's brutal tactics against foe and civilians alike , such as raping , enslaving and selling Iraqi women belonging to the Yazidi religious minority . Last week , a United Nations panel stated what many consider obvious : ISIS has committed war crimes and crimes against humanity in Syria .

Yazidi women ` treated like cattle '

The most high-profile of these abuses -- because they were taped and publicized as propaganda , for all the world to see -- have been the beheadings of ISIS captives . The mother of the first American so killed , journalist James Foley , said that her family is in touch with Kassig 's family and that they are `` heartbroken another American has given his life for the suffering people of Syria . ''

The West is fighting back , with many countries -- including France -- allying with Iraq to conduct airstrikes targeting ISIS in that country . The United States has also led airstrikes going after the group in Syria .

From Monday to Wednesday , for instance , the U.S.-led coalition launched five airstrikes near the northern Syrian city of Kobani and one targeting an oil collection point in al-Hasakah , in addition to a strike targeting a facility purportedly used by the so-called Khorasan Group . There were even more strikes in Iraq , including 13 near Kirkuk , seven near Mosul , three near Baiji and one near Fallujah , according to the U.S. military .

OPINION : Kassig 's murder a sign of weakness from a terror group on the run

ISIS has n't relented much either , including unleashing yet more violence Wednesday .

At least four people died and 29 others were wounded after a vehicle drove up to the entrance to a government building in Irbil , the strongly fortified capital of Iraqi Kurdistan , and exploded , according to Kurdistan Regional Government spokesman Safeen Dizayee . Police `` who tried to stop '' the vehicle were among the dead , he said .

Dizayee added that ISIS -- which is active in northern Iraq -- claimed responsibility for the attack .

Meanwhile , fighting continues in Syria as well , some of it near the Turkish border .

John Allen , the former commander of American forces in Afghanistan now charged with coordinating the coalition to battle ISIS , met with officials in the Turkish capital of Ankara about that fight on Wednesday .

The same day , Turkish President Recep Tayyip Erdogan called for more to be done -- including establishing no-fly zones and bolstering `` train and equip '' efforts for those fighting ISIS . Turkey has spoken out against ISIS , while also expressing opposition to groups of Kurdish fighters that are among those trying to defeat the group .

`` The coalition powers still have not taken these steps we asked for and recommended , '' Erdogan said , according to a report from the semi-official Anadolu news agency . `` We are living this process on small hints and possibilities . ''

CNN 's Laura Akhoun and Marion Lory in Paris , Elizabeth Joseph in Hong Kong , as well as CNN 's Nick Paton Walsh and journalist Zeynep Bilginsoy in Gaziantep , Turkey , contributed to this report .

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Prosecutor : Mickael Dos Santos was wanted by French authorities before video

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U.S.-led coalition strikes ISIS targets around Iraq and Syria , U.S. military says

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France 's President says two French citizens are in latest ISIS beheadings video